Multicomponent organic coating of polyester, polyurethane and a humidity barrier thermoplastic resin

ABSTRACT

An electrophotographic plate having a three component resin composition coating is disclosed. The coating consists of from about 16 to 71 percent film forming polyester, 16 to 71 percent moisture insensitive, film forming, organic solvent soluble resin and 5 to 35 percent polyurethane polymers. The three component resin overcoating exhibits particular utility in that it enables an electrophotographic member to function under conditions of high humidity.

United States Patent Gerace et a1.

[ 1 Oct. 14, 1975 MULTICOIVIPONENT ORGANIC COATING OF POLYESTER,POLYURETHANE AND A HUlVflDITY BARRIER THERMOPLASTIC RESIN Inventors:Paul L. Gerace, Rochester; Paul R.

Handley, Webster; Rudy H. Haidle, Evanston, all of 111.

Xerox Corporation, Stamford, Conn.

Filed: Jan. 5, 1973 Appl. No.: 321,193

Related US. Application Data Continuation-impart of Ser. No. 38,467, May18, 1970, abandoned.

Assignee:

U.S. Cl. 96/1.5 Int. Cl. G03G 5/04 Field of Search 96/l.5, 115; 117/61References Cited UNITED STATES PATENTS 7/1964 Clark 96/1 3,159,48312/1964 Behmenburg 96/1.5 3,312,548 4/1967 Straughan 96/1.5 3,403,0199/1968 Stahly 96/1.5 3,639,120 2/1972 Snelling 96/1.5 3,656,949 4/1972Honjo 96/1.5 3,682,632 8/1972 Fumiaki 96/1.5 3,736,134 5/1973 Gosselinket a1. 96/1.5

Primary Examiner-Norman G. Torchin Assistant ExaminerJohn L. Goodrow[57] ABSTRACT 7 Claims, I Drawing Figure U.S. Patent Oct. 14, 19753,912,511

MULTICOMPONENT ORGANIC COATING OF POLYESTER, POLYURETHANE AND A HUMIDITYBARRIER THERMOPLASTIC RESIN This application is a continuation-in-partof copending application Ser. No. 38,467, filed May 18, 1970, and nowabandoned.

BACKGROUND OF THE INVENTION The present invention relates to xerographyand more particularly to an improved xerographic plate.

The xerographic process described in US. Pat. No. 2,297,691 to ChesterF. Carlson, involves the sensitization of a xerographic plate, as byplacing an electrostatic charge thereon, and the exposure sensitizedplate exposed to an original image to be reproduced. The exposed plateis developed by contacting the plate surface with electrostaticallycharged, finely divided powder particles to produce a powder image whichis either used or fixed in situ or thereafter transferred from the plateto a final support, the transferred image being fixed thereon to formthe final print. If desired, the transfer step may be omitted and theimage fixed to the plate itself. As originally described by Carlson, thexerographic plate consisted of a thin layer of sulfur, anthracene oranthraquinone, either singly or in combination, applied to a relativelyconductive base by melting and flowing onto the base or by evaporatingmaterial onto the base which is kept at a lower temperature so as tocondense the vapor.

A significant advance was made in xerography when it was discovered thatvitreous selenium was highly photoconductive. A selenium xerographicplate generally comprises a metal backing plate, as aluminum, havingcoated on one side, as by vacuum evaporation, a layer of very highpurity viteous selenium. In the dark the selenium layer has a highresistivity, but when exposed to light the resistivity is reduced manyorders of magnitude, the amount depending on the intensity andwavelength of light. By reason of its high electrical resistivity in thedark the selenium layer can be charged electrostatically, which chargeis retained for prolonged periods until light impinges thereon causingdischarge. The outstanding ability of vitreous selenium to hold itscharge for an appreciable period in the dark coupled with its high lightsensitivity have made the selenium plate the standard commercial plateof xerogra phy. Such plates are costly to fabricate, but may be used athousand or more times in the xerographic process so that the cost perimage developed is small. Thus, the selenium plate requires reusabilityto obtain reasonable operating costs.

Another advance was made in the field of xerographic plates with thediscovery of the binder plate. Such plates are described by Arthur E.Middleton in U.S. Pat. No. 2,663,636. As there described it was foundthat an efficient xerographic plate can be obtained by coating arelatively conductive base with a photoconductive insulating compositionprepared by intimately mixing and grinding together any photoconductiveinsulating material, a binder of high electrical resistance and asolvent.

When the binder and photoconductor are selected from low cost materialsand the backing comprises an inexpensive material such as paper, it iseconomically feasible to utilize a xerographic plate, only once, thatis, use it as a disposable xerographic plate. However,

necessarily such a paper is significantly more expensive than non-lightsensitive paper. Therefore, for high volume applications, reusability ofthe xerographic plate is essential no matter whether a uniformphotoconductor is used or a binder composition. In a disposable binderplate, the photoconductor is selected primarily on the basis of cost,rather than on the merits of its xerographic properties. If, however,the plate is reusable, then the cost of the photoconductor is not suchan overriding consideration. Thus, in present commercial xerographyutilizing a reusable plate, as in the vitreous selenium plate, thephotoconductive layer is generally the most expensive as well as themost easily damaged element of the plate.

In high speed, xerographic applications as described for example in US.Pat. No. 2,357,809 to C. F. Carlson it is important to apply aprotective layer or coating over the photoconductive insulating materialso as to extend the life of the plate. Generally, the overcoating isformed by applying a solvent solution of an organic resin to the platesurface and allowing the solution to evaporate. However, there are manyhighly polymerized, solvent resistant resins that cannot be applied bythis method and, further, when a solvent is found for such a polymer itoften has a deleterious effect upon the photoconductor. The solution tothis problem was found by .l. J. Kinsella in U.S. Pat. No. 3,146,145where there is disclosed a process involving placing a thin pellicle ofhighly polymerized, solvent resistant resin in contact with aphotoconductive insulating layer and then subjecting the assembly to ionbombardment in a vacuum.

While various waxes, hydrocarbons, inorganic resins have been employedas a protective layer on reusable xerographic plates, they all have asimilar problem in that their electrical properties change significantlyat very high and very low humidities. Therefore most organic materials,particularly resins, when used as overcoatings on electrophotographicplates affect the quality of the image resolution from said plate whenit is operated at humidities above about 58 percent relative humidity(RH) or below 20 percent relative humidity. This is due to the tendencyof the coating composition to absorb and de-sorb moisture therebyvarying its electrical behavior, i.e. the discharge properties of theplate. Thus it has been found that a common coating such as celluloseacetate which has the property of wear resistance and electricalproperties at a moderate RH is not moisture insensitive in either highor low humidities. Therefore, cellulose acetate is unsuitable for use insystems requiring high image quality under such conditions.

SUMMARY OF THE INVENTION According to the present invention a threecomponent polymer composition now has been found which not only obviatesthe problem of operating xerographic plates in high or low humidity butprovides excellent wear resistance and suitable electrical propertiesfor use in reusable xerography. Therefore when the three componentorganic resin composition of the present invention is used as anovercoating on a xerographic plate there is obtained a reusable platecharacterized by wear resistance, moisture insensitivity, exceptionallyeasy cleaning, and overall efficiency in a repetitive xerographicprocess. The photoconductor in the reusable electrophotographic platecontemplated in the instant invention may be used in the form of acontinuous uniform layer as in the case of vitreous selenium or may bein the form of a binder plate.

DESCRIPTION OF THE INVENTION In general, the electrophotographic plateof the instant invention comprises a photoconductive insulating surfaceovercoated with a thin layer of a three component organic polymercomposition of the present invention. More specifically, the presentinvention involves the use of three organic resins whose physical andelectrical properties are suitable for use as an overcoating for anelectrophotographic plate. The particular components of the coatingcomposition comprise film forming polyesters, which are well known fortheir physical wear resistance, film forming, organic solvent solubleresins having the property of moisture insensitivity, and certainpolyurethanes, having volume resistivities in the range from "10 ohm-cm.The use of these three resins in a coating composition of theelectrophotographic plate involves the discovery that certainconcentration of each component resin will render a coating compositionhaving the physical and electrical properties indigenous to each resinin the composition; that is, the final composition will be wearresistant due to its film forming polyester content, moistureinsensitive due to its content of moisture insensitive, film forming,organic solvent soluble resin, and have suitable electrical propertiesfor use in xerography due to its polyurethane content.

The particular concentration necessary to arrive at the necessaryproperties of the instant overcoating are from about 16 to 71 percent byweight of the moisture insensitive, film forming organic solvent solubleresin, from about 16 to 71 percent polyester, and from about 5 topercent polyurethane having a volume resistivity of from about 10" to 10ohm-cm. It is found that a composition outside of these concentrationsresults in the absence or weakening of one of the three propertiesnecessary for the organic xerographic coating. Particularly critical isthe control of the electrical properties of the coating by addition ofthe proper amount of polyurethane. The electrical requirement necessaryis that sufficient charge dissipation be accomplished through the layerof the coating without sufficient lateral conductivity to produce imagedegradation in the xerographic imaging process. If there is too muchpolyurethane in the three component composition, the coating islaterally conductive while too little renders the coating insulatingwith regard to charge dissipation through the layer. This will bediscussed more fully hereinafter.

The particular moisture insensitive, organic solvent soluble filmforming resins which can be used in the three component composition ofthe present invention include many thermoplastic resins. Typicallyeffective resins include polyvinyl chloride, polyvinyl fluoride,polyvinylidene chloride, polyisobutylene, and copolymers thereof.Preferred resins in the three component resin composition of the instantinvention are vinyl copolymers and copolymers of vinylidene chloride andacrylonitrile.

The film forming polyesters which can be used in the three componentcompositions of the instant invention are those comprised of aromaticdicarboxylic acids with glycols. As a class, these can be described asaromatic, solvent soluble, thermoplastic linear polyester polymers.Typical products would be polymers or copolymers of terephthalic andisophthalic acids with ethylene glycol, trimethylene glycol,tetramethylene glycol, pentamethylene glycol and hexamethylene glycol.The preferred composition would be a copolymer of terephthalic andisophthalic acids with ethylene glycol. One example of a typicalpolyester is Vitel PE200, which is a high molecular weight, linearpolyester solution resin manufactured by the Chemical Division ofGoodyear Tire and Rubber Company. It is a copolymer of terephthalic andisophthalic acids with ethylene glycol.

The polyurethane resins to be used in the three component resincomposition of the present invention include any polyurethane elastomerwhich has a volume resistivity of from about 10 to 10 ohm-cm and isprepared by the basic reaction of an isocyanate with an alcohol or anester. Typical of those polyurethanes to be used within the purview ofthe present invention include those prepared by the reaction of toluenediisocyanate or diphenylmethane-4,4'-diisocyanate with any alcohol. Oneexample of a typical polyurethane is Vithane TPU123 which is athermoplastic solvent soluble polyester-based polyurethane elastomermanufactured by the Chemical Division of Goodyear Tire and RubberCompany. Another typical polyurethane is Estane 5702-F2 having a similarcomposition to Vithane TPU123, and which is manufactured by the B. F.Goodrich Company.

DESCRIPTION OF THE DRAWINGS FIG. 1 represents the xerographic plateaccording to the instant invention.

As shown the figure illustrates a xerographic plate 10, which comprisesan electrically conductive base 1 1 having coated at least one sidethereof a layer of photoconductive insulating material 12. Thephotoconductive insulating layer-may comprise selenium, selenium alloys,organic photoconductor material, or a binder layer such as thatillustrated in US. Pat. No. 2,663,636 to Middleton. On top of thephotoconductive insulating layer is the three component resincomposition of the present invention designated as 13. The compositionas described hereinbefore comprises polyester resin,

moisture insensitive, film forming, organic solvent soluble polymer, andpolyurethane resin. The thickness of the three component overcoating ofthe present invention may range from about 0.5 to 5 microns.

To illustrate the instant invention 60 grams of Saran F310, a copolymerof vinylidene chloride and acrylonitrile, produced by the Dow ChemicalCompany of Midland, Michigan is dissolved in 1000 milliliters ofcyclohexanone and 1500 milliliters of ethoxy-ethanol with stirring overa 2 hour period. A gram portion of a film forming polyester produced bythe Goodyear Company of Akron, Ohio, under the tradename Vitel PE 200 isdissolved in a mixture of 800 milliliters of toluene and 1200milliliters of cyclohexanone by stirring over a 3 hour period. Asolution of polyurethane is then effected by slowly adding 35 grams of apolyurethane elastomer produced by Goodyear Company of Akron, Ohio,under the tradename TPU 123, and having a volume resistivity of about 10ohm-cm., in 700 milliliters of dimethyl formamide over a two hour perioduntil complete solution takes place. The three solutions are addedtogether and additional solvent is added when.

necessary to prevent reprecipitation of one of the resins. When axerographic selenium drum is dip coated with the resulting solution, athin coating is formed which physically resembles a pattern ofdifferentially phased dots dispersed in a binder. The resultingxerographic plate comprises an aluminum substrate, a layer of amorphousselenium of about 20 microns thick and a 2 micron thick layer of a threecomponent resin composition of the present invention. It is found thatthe three component resin overcoated xerographic plate of the presentinvention can be imaged in humidity conditions of from about 6 to 95percent relative humidity.

The general scope and nature of the invention having been set forth thefollowing examples are given as typical illustrations of the inventionand are not by way of limitation.

EXAMPLE I The three component resin composition of the present inventionis prepared in the following manner: An 80 gram portion of GoodyearVite] polyester 200 is dissolved in a solution of 240 milliliters (mls.)of methylethyl-ketone, 240 mls. of 2-methoxy ethyl acetate, 220 mls. oftoluene, 1200 mls. of xylene and 800 mls. of cyclohexanone by stirringover a three hour period.

A second solution is prepared by dissolving 25 grams of solid TPU 123, apolyurethane manufactured by the Goodyear Company, and 667 millilitersof dimethylformamide. Complete solution also takes place over a threehour period by slowly adding and stirring the solid polyurethane anddimethyl formamide (DMF) over the three hour period.

A third solution is prepared by dissolving 50 grams of Saran F310, acopolymer of vinylidene chloride and acrylonitrile, manufactured by theDow Chemical Company of Midland, Michigan, in a thousand mls. ofcyclohexanone and 1533 mls. of 2-ethoxy ethanol. Solution again isobtained by stirring over a three hour period the solvent systemcontaining Saran.

After complete solution of the various resins is completed in the threehour mixing period, the polyurethane solution and the Saran solution arethen added together and stirred for a period of one hour. During thistime there is no indication of reprecipitation of either resin.Thereafter the polyester solution is added to the polyurethane-Saranmixture which results in a cloudy solution thereby indicatedreprecipitation. Thereupon 6400 mls. of toluene is slowly added alongwith 1600 milliliters of dimethylformamide (DMF) where upon completedissolution of the three resins is affected.

A xerographic flat plate comprising an aluminum substrate overcoatedwith a 60 micron layer of an arsenic-selenium alloy, having acomposition of 0.5 percent arsenic, 99.5 percent selenium which ishalogen doped with 10 parts per million chlorine, is prepared in theconventional manner as outlined in US. Pat. No. 3,312,548 to Straughan.The plate is then dip coated with the three component resin solutionprepared above by means ofa dip coating apparatus and dried in anexhausted laminar flow hood. There results a xerographic plate havingapproximately a two micron overcoating comprising the three resins whichwere prepared in solution above. Physically, the three component resinovercoating appears as a dot pattern of differentially phased spheresdispersed in a matrix.

EXAMPLE n A solution of cellulose acetate is prepared by dissolvinggrams of cellulose acetate in 2000 mls. of ethylene-dichloride. Axerographic flat plate having the same composition as that of Example Iis dip coated in the cellulose acetate solution using a Fisher Painecoater and dried in an exhausted laminar flow hood. There results axerographic plate having a two micron layer of cellulose acetateovercoating.

EXAMPLE III The plates prepared in Examples I and II were then placed ina controlled environment having a relative humidity of 60 percent andstored under these conditions for a period of 2 days. Both plates werethen removed and placed in a xerographic copy apparatus sold by XeroxCorporation under the tradename Model D Processor under a controlled RHof 60 percent where they are charged to 800 volts and exposed to astandard pattern. The xerographic copy produced by the plate prepared inExample I showed excellent reproduction, especially with respect to theresolution of the lines in the pattern. The copies made by the plateprepared in Example II, however, demonstrate a degradation of imagequality indicating lateral conductivity of the overcoating caused by thehigh moisture environment.

The plate prepared in Example I also indicated good adhesion to thesurface of the photoreceptor in that it could not be removed by adheredcellophane tape. It also demonstrated good wear resistance bywithstanding 10,000 dynel brush abrasion cycles.

In an effort to further exhibit the superiority of the three componentovercoating of the present invention, xerographic plates were made usingovercoatings of the three components separately, and two xerographicplates were made containing an overcoating of the present invention.These plates were then tested to compare and evaluate x-ray imageresolution, transfer of toner image, and the cleaning qualities of theplates. The test procedures and test data are as follows:

TEST PROCEDURES FOR X-RAY IMAGE RESOLUTION, TRANSFER AND CLEANING PlateStructures Five xerographic plates are made according to the method setforth in Example I. The plates comprise a micron vitreous layer of 99.66weight percent selenium 0.34 weight percent arsenic contained on a 9%inch X 14% inch X 0.081 inch aluminum plates. Plates designated Nos. 1A,2A and 3A are overcoated with a 1 micron layer of polyurethane,vinylidene chlorideacrylonitrile copolymer (Tradename Saran F-3l0), andpolyester, respectively. Plate 4A is overcoated with a one micron layerof 10 percent polyurethane balance 1.6 parts polyester to 1.0 partsvinylidene chloride-acrylonitrile copolymer. Plate 5A is overcoated witha one micron layer of 16 percent polyurethane balance 1.6 partspolyester to 1.0 parts vinylidene chloride-acrylonitrile copolymer. Bothplates 4A and 5A are directed to a three component overcoating of thepresent invention, while plates 1A, 2A and 3A are overcoated with 100percent of a single component of the three components of the overcoatingcomposition of the invention.

X-Ray Image Resolution Test An overcoated test plate is inserted into anupdated Xerox Model D Processing Unit and scorotron charged to 1600volts positive potential. The plate is covered to prevent light exposureand transferred while so charged to a Picker Model 815 X-ray Unit. Theplate is then ex posed through an aluminum step wedge test target to25.5 KVP radiation for 400 milliamp seconds. The aluminum step wedgetarget contains line pairs and grid patterns in a range from 2 to 10.The higher the number of lines and grids observed, the better theresolution. If none of the patterns are discernible, the resolution issaid to be zero. Normally the resolution patterns are read with the aidof 4X eyepiece magnification.

Image Transfer Test ferred image is permanently affixed to the paper bymeans of heat or methylene chloride vapor fusing.

Cleaning Test The photoreceptor plate is then cleaned by inserting itinto brush cleaning apparatus whereupon it comes into contact with arotating dynel brush at the entrance. The cleaning must be accomplishedby 2 passes of the brush over the plate. One pass occurs as the plate isinserted into the apparatus and the other pass as the plate is removed.The cleaned plate is then visually inspected for the presence ofresidual toner.

The results of the x-ray resolution, image transfer and cleaning testsare tabulated in Table I.

As shown in Table I, the three component overcoatings of the presentinvention (plates 4A and 5A) exhibit superior properties with regard tox-ray image resolution, transfer of toner image, and cleaning, while thethree components, when used separately as overcoatings (plates 1A, 2Aand 3A), are inferior in at least one of the three tests.

In order to demonstrate the degree of abrasion resistance which thethree component overcoatings of the present invention exhibit over thecomponents of the overcoating separately, the following tests arecarried out:

ABRASION RESISTANCE TEST CONDITIONS Eight plates numbered 18, 2B, 3B and58 (there are two No. lBs, two No. 2Bs, etc.), respectively, are made bycoating a glass plate with a thin layer of the overcoating materialonly. The plate numbers correspond to the overcoating material usedunder the heading plate structure in Exhibit II. The plates are made andtested as follows:

Two 2 inch by 2 inch glass plates are each dip coated with theappropriate overcoating material. The coating thickness is roughly onemicron. One sample of each of the overcoated plates is then separatelytested by abrading with a sand dropping device (Gardner Falling SandAbraser, Gardner Labs, Inc., Bethesda, Md.) in which Ottawa sand isdropped from a height of about 36 inches onto the appropriate platewhich is placed at an angle of about 45 to the falling sand. By theimpact of the sand particles, a very small amount of the overcoatingmaterial is worn off the substrate. In addition, the surface of theovercoating exhibits some pit marks and scratches which are also formedby the abrading sand. The more resistant coatings show less marks, ofcourse, after the sand test. The degree of surface deterioration can bemeasured by a haze meter. The haze meter measures the percent of lighttransmitted which is deviated from the incident beam by forwardscattering. The more pitmarks a surface has, the more light isscattered, therefore, the higher the reading on the haze meter. Anunabraded sample with a smooth surface shows a very low haze value.Therefore, the percentage of haze which is produced by the sand is themeasure of the abrasion resistance of the coating.

TABLE I COMPARATIVE DATA Image Resolution Plate No.* OvercoatingComponent X-Ray Exposure Transfer of Toner Image Cleaning of Plate 1AAll polyurethane 3 fair Requires Additional Requires Additional ProcessStep (i.e. Process Step (Le. Reverse Charging) Negative Preelean) 2A AllVinylidene 0 poor Good Cannot be Cleaned Chloride-AcrylonitrileInitially Toner (Saran F-3l0) Will Not Come Off Overcoating 3A Allpolyester 3 fair Good Good 4A Present Invention 4 good Good Good (10%Polyurethane Balance 1.6 Parts Polyester to 1.0 Parts VinylideneChloride-Acrylonitrile Copolymer) 5A Present Invention 6 excellent GoodGood (16% Polyurethane Balance 1.6 Parts Polyester to 10 PartsVinylidene Chloride-Aerylonitrile Copolymer) Each plate contains a I30micron layer M99136 weight percent selenium 0.34 weight percent arsenicon a 9V4" X 14%" aluminum substrate. Each plate has a differentovercoating component about I micron in thickness.

In the specific test, a sample of each of the different overcoatingcompositions is abraded by milliliters of falling sand. Then thesesamples, together with identical control samples of each compositionwhich had not been abraded, are measured with a Werner and PfleidererCorporation Model TRBI Haze Meter. These results are tabulated in TableII. The abraded samples showed an increase in haze value, and bycalculating the difference in haze value from abraded and unabradedsamples of each composition. Plate 58 of the present invention showedthe least abrasion, a 2 percent increase in haze value, while thepolyester showed a 3.5 percent increase, the Saran an 8.5 percentincrease and the polyurethane a 10 percent increase.

TABLE II COMPARATIVE DATA Abrasion Resistance Increase In Haze AfterAbrasion Plate No. Plate Structure With respect to abrasion resistancedata shown in Table II, the plate designated 58 has the overcoating ofthe present invention, and when compared to plates 1B, 2B and 3B, whichemploy overcoatings of the three component separately, the abrasion, orincrease in haze after abrasion, was extremely low in case of, the threecomponent overcoating. When each of the three overcoating components areused separately, however, (plates 13, 2B and 3B) they exhibitsignificant abrasion or increase in haze after abrasion.

The solvent system for the three component resin coating composition ofthe present invention may comprise any of the commercially availablesolvents well known to those skilled in the art. These include suchsolvents as methyl-ethyl-ketone, 2-ethoxy ethyl acetate, toluene,xylene, cyclohexanone, dimethylformamide, and Z-ethoxy ethanol.Complexity of the solvent system results from parameters such atemperature and quantity of the ultimate composition and techniques forsimplification by using multiple quantities of presently availablesolvents is well known to those skilled in the art.

Without intending to limit the scope or spirit of the present threecomponent resin coating composition by proposing a theory, anexplanation is speculated as to the function of the present compositionunder conditions of high or low humidity. It is well known that underconditions of high humidity most resin compositions undergo significantincrease in both their lateral and vertical conductivity; that is,charge dissipation occurs both across and through the overcoating. It isbelieved, however, that the present three component resin compositionundergoes virtually no change in either its vertical or lateralconductivity at high or low humidities. It is speculated that thisphenomena is due to the nature of the three component composition inthat the differentially phased clots, hereinbefore re ferred to, arespheres of polyurethane distributed throughout the film matrix. Becausethe particles of polyurethane remain relatively protected by the binderfilm the electrical properties of the overcoating remain relativelyunchanges at low or high humidities.

It is further speculated, without intention of limitation, that in thefunction of the three component resin composition of the presentinvention the spheres of dispersed polyurethane conduct charges throughthe resin overcoating. Therefore upon charging a three componentovercoated xerographic plate, the charge is dissipated through thethickness of the overcoating layer and remains at the interface of theovercoating and photoreceptor layer. Upon exposure the charges in theilluminated area will then be dissipated through the photoreceptor layerwhile those unexposed areas would retain charges at the interface.Because the thickness of the layer is no more than about 5 microns, nodifficulty of electroscopic particle development is presented.

Selenium being the photoconductor of choice in commercial xerography, itis preferred to use the instant three component resin overcoating withselenium. However, the nature of the photoconductive insulating layer isnot critical so that the coating may be used with any photoconductiveinsulating material such as selenium alloys (Se-Te, Se-As, etc.),anthracene, and other continuous films in binder plates describedhereinbefore. As is wellknown in the xerographic art, any electricallyconductive support layer may be used for the photoconductive insulatinglayer. Alloy selenium plates are often constructed in a layer structurewhere a thin alloy layer, as for example, selenium-tellurium, orselenium-arsenic, is coated on a layer of vitreous selenium thuscombining excellent photoresponse of the alloy with the excellentelectrical characteristics of uiteous selenium. Such plates aredescribed for example in U.S. Pat. No. 2,803,541 to Paris. In addition,the three component resin composition of the present invention may beused in any xerographic plates known to those skilled in the art. Suchplates are described as to preparation, composition, thickness, andother parameters, for example, in U.S. Pat. No. 2,803,542 to Ullrich;U.S. Pat. No. 2,803,541 to Paris; U.S. Pat. No. 2,745,327 to Mengali;U.S. Pat. No. 2,863,768 to Schaffert; U.S. Pat. No. 2,970,906 to Bixby;and aforesaid patents to Middleton and Reynolds.

It is to be understood that various modifications known to those skilledin the art can be made to the present, three component resin compositionwithout departing from the spirit of the invention. For example,substances may be added to enhance or synergize the properties of thethree component resin composition coating.

What is claimed is:

1. An electrophotographic plate comprising:

a. a photoconductive insulating layer contained on a conductivesubstrate, and

b. an organic polymer coating composition overlaying the saidphotoconductive layer, said coating composition comprising from about 16to 71 percent of a film forming polyester; about 16 to 71 percent of amoisture insensitive, film forming or- 5. The plate of claim 1 in whichthe moisture insensitive, film forming, organic solvent soluble resin isa copolymer of vinylidene chloride and acrylonitrile and thepolyurethane has a volume resistivity of from about 10 to 10 ohm-cm.

6. The plate of claim 1 in which the polymers are present in thecomposition of from about 51 percent film forming polyester, about 32percent moisture insensitive film forming, organic solvent solubleresin, and about 17 percent polyurethane resin.

7. The plate of claim 1 in which the thickness of the polymerovercoating is from about 0.5 to 5 microns.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIQNDATED October 14 1975 INVENTOR(S) Paul L. Gerace, Paul R. Handley RudyH. Haidle It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 36, delete "viteous" and insert -vitreous-.

Column 2, line 44, delete "de-sorb" and insert --desorb-.

Column 9, Table II, Plate No. 5, delete "vinylidend" and insertvinylidene-.

Column 9, line 49, delete methyl-ethyl-ketone" and insert-methylethylketone.

Column 10, line 9, delete. "unchanges" and insert unchanged-.

Column 10, line 33, delete "wellknown" and insert well known.

Column 10, line 41, delete uiteous" and insert vitreous-.

Signed and Scaled this twenty- D 3) Of January 19 76 [SEAL] A ttes t:

RUTH Cr MASON C. MARSHALL DANN Arresting Officer Commissioner oj'Patentsand Trademarks

1. AN ELECTROPHOTOGRAPHIC PLATE COMPRISING: A. A PHOTOCONDUCTIVE INSULATINGG LAYER CONTAINED ON A CONDUCTIVE SUBSTRATE, AND B. AN ORGANIC POLYMER COATING COMPOSITION OVERLAYING THE SAID PHOTOCONDUCTIVE LAYER, SAID COATING COMPOSITION COMPRISING FROM ABOUT 16 TO 7U PERCENT OF A FILM FORMING POLYESTER, ABOUT 16 TO 71 PERCENT OF A MOISTURE INSENSITIVE, FILM FORMING ORGANIC SOLVENT SOLUBLE THERMOPLASTIC RESIN SELECTED FROM THE GROIP CONSISTING OF POLYVINYL CHLORIDE, POLYVINYL FLUORIDE, POLYVINYLIDENE CHLORIDE, POLYISOBUTYLENE, AND COPOLYMERS THEREOF, AND FROM ABOUT 5 TO 35 PERCENT OF A POLYURETHANE RESIN, WITH SAID POLYURETHANE RESIN HAVING A VOLUME RESISTIVITY OF FROM 10**11 TO 10**13 OHM-CM.
 2. The plate of claim 1 in which the photoconductive insulating material is amorphous selenium.
 3. The plate of claim 1 in which the photoconductive insulating material is an arsenic-selenium alloy.
 4. The plate of claim 3 in which the alloy is doped with a halogen.
 5. The plate of claim 1 in which the moisture insensitive, film forming, organic solvent soluble resin is a copolymer of vinylidene chloride and acrylonitrile and the polyurethane has a volume resistivity of from about 1011 to 1013 ohm-cm.
 6. The plate of claim 1 in which the polymers are present in the composition of from about 51 percent film forming polyester, about 32 percent moisture insensitive film forming, organic solvent soluble resin, and about 17 percent polyurethane resin.
 7. The plate of claim 1 in which the thickness of the polymer overcoating is from about 0.5 to 5 microns. 